In preparing certain substrates it is important that at least one surface have a smooth finish. Often this smooth finish requires very high tolerances. Prior art solutions to the problem of creating a smooth finish have not been completely satisfactory. One prior art solution has been to use elastomeric rollers. Elastomeric rollers, however, cannot be ground to the same high tolerance as metallic rollers.
Another prior art solution has used carrier webs having a smooth surface finish as a backing material for the substrate as it passes through the nip. A problem with this solution is that the carrier web usually must be discarded or recycled adding to the cost of the manufacturing process. Another problem is that the carrier web often wrinkles.
Using a roller having a metal sleeve with a smooth surface finish over an elastomeric backing is a possibility. This solution, however, also has drawbacks. The thin metal sleeve is subject to cracking after repeated use, especially along the margins.
One prior art solution is discussed in U.S. Pat. No. 5,146,664 (Biondetti). The solution proposed is a series of hydraulic pistons. These hydraulic pistons, however, operate on a thick outer shell to correct for beam deflections in the roller. An apparatus as disclosed would be expensive and not suitable for all applications.
For a patterned roller, a rapid pressure rise at a nip is important to force material to the pattern. Metallic shells of small diameter inherently will create a small nip footprint, for a given nip load, which results in a higher pressure. In the formation of extrusion cast web materials the nip action improves the replication of the polished or patterned roller surfaces.
In an ideal situation, rollers would be perfectly cylindrical and the molten resin would be uniformly distributed. In practice, neither condition is achieved. An ability to locally adjust roller shape is desirable to improve cross width nip loading. Consequently the web material will have more consistent thickness and surface uniformity. Self adjusting rollers are utilized in paper manufacturing or web calendaring operations which require high nip loads, but they have minimal heat transfer capabilities.
It is desirable to have a roller capable of creating a smooth finish, with a small nip footprint, having an improved heat transfer capability, and capable of adjustment.